9. Stock-Based Compensation

Equity Incentive Plans

In September 2012, the Company adopted the 2012 Equity Incentive Plan, as amended, which provides designated employees of the Company and its affiliates, certain consultants and advisors who perform services for the Company and its affiliates, and nonemployee members of the Board of Directors of the Company and its affiliates with the opportunity to receive grants of incentive stock options, nonqualified stock options and stock awards.

On January 20, 2017, the Company's stockholders approved the 2016 Equity Incentive Plan (the "2016 Plan"). Beginning on January 1, 2018, the number of shares of common stock authorized for issuance pursuant to the 2016 Plan was increased each January 1 by an amount equal to four percent (4%) of the Company's outstanding common stock as of the end of the immediately preceding calendar year or such other amount as determined by the compensation committee of the Company's board of directors. During the year ended December 31, 2019, the compensation committee of the board of directors authorized an additional 3,000,000 shares of common stock to be added to the shares authorized for issuance under the 2016 Plan.

As of December 31, 2020, there were 340,144 shares available for grant under the Company’s Equity Incentive Plans.

A summary of stock option activity under the Company’s Equity Incentive Plans is as follows:


		Weighted
		Average		Weighted	Aggregate
		Exercise Price		Average Remaining	Intrinsic
	Options	Per Share		Life in Years	Value
Outstanding at December 31, 2018	2,761,912	$	11.30	8.01	$	—
Granted	1,481,975	$	1.48
Forfeited	(219,321)	$	15.14
Outstanding at December 31, 2019	4,024,566	$	7.48	7.98	$	2
Granted	2,662,500	$	2.10
Exercised	(32,778)	$	1.53
Forfeited	(260,435)	$	6.95
Outstanding at December 31, 2020	6,393,853	$	5.29	7.96	$	1,961
Options exercisable at December 31, 2020	3,482,169	$	7.83	7.07	$	722
Options vested and expected to vest at December 31, 2020	6,393,853	$	5.29	7.96	$	1,961

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and directors during the years ended December 31, 2020 and 2019 were as follows, presented on a weighted average basis:


	Year Ended December 31,
	2020		2019
Expected volatility	66.94	%	66.94	%
Weighted average risk-free interest rate	0.66	%	2.07	%
Expected dividend yield	0.00	%	0.00	%
Expected term (in years)	6.85		6.77

Stock options generally vest over a three or four year period, as determined by the compensation committee of the board of directors at the time of grant. The options expire ten years from the grant date. As of December 31, 2020, there was approximately $3,947 of unrecognized compensation cost related to non-vested stock options, which is expected to be recognized over a remaining weighted-average period of approximately 2.08 years.

The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees in the consolidated statements of operations as follows:


	Year Ended
	December 31,
	2020		2019
Research and development	$	1,028	$	714
General and administrative		1,296		3,018
Total	$	2,324	$	3,732

Restricted Stock Units

During the years ended December 31, 2020 and 2019, the Company issued 92,500 and 181,000 restricted stock units (“RSUs”), respectively, to employees under the 2016 Plan. Upon vesting of the RSUs, the Company has the option to settle the award by either issuing shares of the Company's common stock or paying an amount of cash equal to the fair value of the Company's common stock on the settlement date. During the years ended December 31, 2020 and 2019, the Company recorded stock based compensation expense related to liability classified RSUs of $204 and $265, respectively. In each of October 2019 and January 2020, the Company cash settled 90,500 RSUs. In January 2021, the Company cash settled 92,500 RSUs. As of December 31, 2020 and 2019, these RSUs are classified as restricted stock liability in the consolidated balance sheets of $204 and $159, respectively, as they contain a cash settlement option.

During the year ended December 31, 2020, the Company granted 660,606 RSUs to an executive officer that will cliff vest and will be settled after three years of continuous service, or upon a change of control of the Company, whichever is earlier, pursuant to the 2016 Plan. During the year ended December 31, 2020, the Company recognized $248 of stock based compensation expense related to equity classified RSUs, as they do not contain a cash settlement option.

The following table presents a summary of outstanding RSUs under the 2016 Plan as of December 31, 2020:


		Weighted
	Number of	Average
	Shares	Fair Value
Outstanding at December 31, 2018	—	$	—
Awarded	181,000	$	1.74
Settled in cash	(90,500)	$	1.17
Outstanding at December 31, 2019	90,500	$	1.76
Awarded	753,106	$	1.49
Settled in cash	(90,500)	$	1.76
Outstanding at December 31, 2020	753,106	$	1.52

As of December 31, 2020, there were 753,106 shares outstanding covered by RSUs that were vested and expected to vest. The weighted average grant date fair value of these shares of restricted stock was $1.49 per share and the aggregate grant date fair value of these shares of restricted stock was approximately $1,112. As of December 31, 2020, there was approximately $690 of unrecognized compensation costs related to RSUs granted to employees, which are expected to be recognized as expense over a remaining weighted average period of 2.21 years.